1. Field of the Invention
The invention relates to an electrical fuse structure, and more particularly, to an electrical fuse structure with improved blowing window.
2. Description of the Prior Art
As semiconductor processes become smaller and more complex, semiconductor components are influenced by impurities more easily. If a single metal link, a diode, or a MOS is broken down, the whole chip will be unusable. To treat this problem, fuses can be selectively blown for increasing the yield of IC manufacturing.
In general, fused circuits are redundant circuits of an IC. When defects are found in the circuit, fuses can be selectively blown for repairing or replacing defective circuits. In addition, fuses provide the function of programming circuits for various customized functions. Fuses are classified into two categories based on their operation: thermal fuse and electrical fuse. Thermal fuses can be cut by lasers and be linked by laser repair. An electrical fuse utilizes electro-migration for both forming open circuits and for repairing. The electrical fuse for semiconductor devices may be classified into categories of poly electrical fuse, MOS capacitor anti-fuse, diffusion fuse, contact electrical fuse, contact anti-fuse, and the like.
A blowing mechanism of conventional electrical fuse is shown in FIG. 1. The cathode of an electrical fuse structure 1 is electrically connected to the drain of the transistor as a blowing device 2 (or referred to be as a driver) and. Voltages Vfs, Vg, and Vs are applied on the anode of the electrical fuse structure 1, the gate of the transistor, and the drain of the transistor, respectively. The source of the transistor is grounded. The electric current is traveled from the anode of the electrical fuse structure 1 to the cathode of the electrical fuse structure 1; and the electrons flow from the cathode of the electrical fuse structure 1 to the anode of the electrical fuse structure 1. The electric current suitable for the blowing is in a proper range. If the electric current is too low, the electron-migration is not completed, whereas if the current is too high, the electrical fuse tends to be thermally ruptured. In general, the blowing current for an electrical fuse structure made by a 65 nm manufacturing process is about 13 mA. The blown region of an electrical fuse also varies according to the design of the product. For instance, the blown region of a contact electrical fuse typically is located in the plug disposed on the cathode region, whereas the blown region of a poly electrical fuse is located in the polysilicon layer of the fuse element.
In conventional art, a predetermined voltage is typically calculated before the fuse structure is blown by voltage values above the predetermined voltage. Unfortunately, the aforementioned poly electrical fuses are unable to be blown by voltage values above the predetermined voltage while not exceeding the predetermined voltage by a lot, which ultimately produces poor blowing window. Therefore, how to fabricate a fuse structure with improved blowing voltage range has become an important task.